This isn't an individual's problem; as much as one might want to pin the blame on one person, that is only a half-conclusion, because it doesn't prevent future manipulation of the system by any other person who might want to come along and do the same thing. What it is, is a design flaw of reddit's voting system, of any voting website that allows anonymous voting in which users are not tied 1-to-1 to their real world identity or otherwise ensures "1 man, 1 vote" (and even that might not go far enough to be considered "fair" for link submissions, because of the way reddit's ranking algorithm heavily magnifies the influence of the first few votes on them).
Do astroturfers paid to push specific agendas exist on reddit? Advertisers or PR firms disguised as users? It doesn't matter if they do or don't yet in reality, they have the incentive and potential to exist within the voting, comment posting, and link posting behavior reddit allows, which is bad enough, reason enough to not place trust in that system.
On the other hand, measures to prevent this type of manipulation can throttle the usefulness of the website or voting framework. And while unrestricted anonymity can breed a diverse range of ideas, it too can be "manipulated" by other techniques, like the brute force spamming of the same message lowering the signal-to-noise ratio of all other opinions, or through other means. I'm sure these issues and others have been discussed to death here.
I think Hubski's been fairly unaffected so far (though low vote manipulation alone still is not a guarantee of all the Important Things (TM) we want in such a site, like high discussion quality) mainly because of "security through obscurity"- it's not popular enough to be often targeted by these entities yet. However, we should recognize another key feature hubski allows: the ability to choose to see "unpopular" or "not-yet-popular" content, as in submissions with empty or near empty hubwheels. Being "downvoted to oblivion" has no parallel (I think?) on hubski because of this, and that may take away half of the problem.